Electrical membrane switches are fabricated by laminating together several layers. A typical membrane switch has at least a base layer, a top layer and an adhesive layer sandwiched between the base layer and the top layer. The adhesive layer has apertures in it which correspond to the locations of electrical switches and other devices. Some more complicated membrane switch structures are made from 5 or more laminated layers.
In fabricating membrane switches it is important to maintain accurate relative alignment between the different layers. Maintaining such registration is complicated by the fact that the layers are adhesively bonded together. The layers stick to each other as soon as they are brought into contact with their adhesive surfaces exposed. Therefore the layers must be accurately aligned as they are brought together.
It is also very important to prevent air from being entrapped between the layers as they are laminated together. The presence of air bubbles can lead to the eventual malfunction of a membrane switch and can also adversely effect the appearance of a membrane switch.
Various techniques and apparatus have been used in the fabrication of membrane switches and similar laminated structures. A significant problem is that such techniques are undesirably slow, insufficiently accurate, or require skilled craftsmanship to practice. There have been some previous attempts to fabricate automated apparatus for building laminated structures. Such apparatus has generally been unsatisfactory.
One prior device known to the inventors had a curved rigid vacuum platen located above a flat vacuum platen. One sheet of a laminated structure could be placed against a guide on the flat platen. Another sheet of the laminated structure could be placed against a guide on the curved platen. The sheets could be held in place by a vacuum. The apparatus could then be operated to cause the curved platen to press against and to roll across the flat platen, thereby pressing the two sheets together. This device had significant problems. The curved platen interfered with easily and accurately aligning the lower sheet on the flat platen. It was difficult to accurately align the top sheet on the curved platen. Furthermore, the trailing edge of the curved platen would lift free of the top sheet as the curved platen travelled across the flat platen. This caused a loss of vacuum in the curved platen which could result in the top sheet falling onto the bottom sheet and trapping air bubbles between the sheets.
There is need for apparatus and methods for quickly and accurately laminating together the sheets which form a laminated structure, such as a membrane switch.